IAC troubles

Cougar V6 99 duratec 2.5

Have annoying problem with high rpm in idle. Happens usually after accelerating and letting go of the pedal the iac quickly rises to around 80% resulting in rpm around 3500. After ca 4-5 seconds the iac again drops to ca 40% and it reaches the desired Rpm around 800. The tp_v is 0,94v when pedal not touched. Seems to me the problem lies in the software or something else is wrong. Can anybody help me.
I have a video of the data variables.

As a rule of thumb under 1v is good but just to be sure Look for a tps pid showing closed throttle or part throttle will say C/T or P/T

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Hi Ben
Thanks for reply.
I dont have partial closed tp’s pids in my scantool. I have a pid that shows the lowest tp_v stored in pcm. Anyways i’ve attached a scan that shows the problem.
What could make the iac go high rpm when pedal is not pressed and the desired rpm is low as well?
It makes no sense to me why the iac sometimes skyrockets both during drive and in neutral, resulting in annnoying high rpm.
Br Peter



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Hey PeterC! To be clear, the TPS is the green trace in your capture? Also, is this Cougar a manual or automatic transmission?

These IAC's are very well known for sticking open at will, so that'd be my first suspicion. The next time you can catch it idling high, try hopping out and tapping on the IAC itself with a screwdriver. If you get an immediate drop in RPM, you know the valve was binding internally.

If you do go to replace the IAC, use a Motorcraft part and nothing else. Aftermarket parts are trash garbage, and will likely give you the same problem you're already having. Clean the throttle body at the same time, if you haven't already. Disconnect the battery for a few minutes to clear the KAM and let the PCM relearn it's idle strategy.

It is a manual european version e.g. a Ford Cougar.

Yes the green line is tps.
Actually i did change iac some time ago. The strange thing was that the new part (not a Motorcraft though) had the exact same problem, but after putting some grease on, the problem would go away, until it comes back after a few days. So yes, that indicates a mechanical fault, also it never happens when engine is cold.. But doesn’t the data show the opposite e.g. that the pcm commands the iac to stay open?

PeterC wrote: It is a manual european version e.g. a Ford Cougar.

Yes the green line is tps.

Gotcha, thank you!

Actually i did change iac some time ago. The strange thing was that the new part (not a Motorcraft though) had the exact same problem, but after putting some grease on, the problem would go away, until it comes back after a few days.

Interesting. Were you doing anything else to the car while lubing the IAC?

But doesn’t the data show the opposite e.g. that the pcm commands the iac to stay open?

Yeah, that's where I'm a bit uncertain, as the manual versions of this car are rare in the States. I've only ever seen one, and didn't have the opportunity to look at scan data. This is why I hesitate to say if the command is abnormal, or just part of the manual transmission idle strategy. 60% is a high command, but I'm not sure it's high enough to cause a 2800 RPM idle.

Another check you could do would be to get it idling high, and disconnect the IAC connector. If the idle drops, the wider opening of the IAC was commanded. If it doesn't, the valve is stuck.

When trying to fix the issue, done it more than a few times , i did this procedure.
1.disconnected the battery
2. Removed the idle air motor
3. Used carb cleaner and a soft brush
4. Let it dry
5. Applied some lube. Tried both wd40 and some thicker stuff like grease.
The procedure seems to remedy the issue for 1-2 weeks. But im getting tired of doing this.

Interesting with test maybe i can try it but difficult as the issue is always when driving e.g.after accelerating. I’ve only tried disconnecting the iac plug when it idles normally, which resulted in the engine stopping, so it does it jobs properly sometimes
Thanks for your suggestions. I am leaning towards buying a new oem iac now. E.g www.amazon.co.uk/Motorcraft-CX1897-Idle-...=8-1&keywords=Cx1897